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9. (a) Hyperthyroidism is caused by an overactive thyroid gland - Edexcel - GCSE Biology - Question 9 - 2020 - Paper 1
Question 9
9. (a) Hyperthyroidism is caused by an overactive thyroid gland. Figure 14 shows a person with a normal thyroid gland and a person with hyperthyroidism. (i) State o... show full transcript
Worked Solution & Example Answer:9. (a) Hyperthyroidism is caused by an overactive thyroid gland - Edexcel - GCSE Biology - Question 9 - 2020 - Paper 1
Step 1
Step 3
Explain how negative feedback, involving the thyroid gland, controls metabolic rate.
Answer
The regulation of metabolic rate is achieved through a negative feedback loop involving the thyroid gland. When the metabolic rate is too high, the brain detects this change, signaling the pituitary gland to reduce the secretion of Thyroid Stimulating Hormone (TSH). This reduces thyroxine production from the thyroid gland, thereby lowering the metabolic rate back to normal levels. Conversely, if the metabolic rate is too low, TSH secretion increases, stimulating more thyroxine production, raising the metabolic rate.
Step 4
Explain how hormones control the menstrual cycle.
Answer
The menstrual cycle is regulated by a complex interplay of hormones, primarily involving the hypothalamus, pituitary gland, and ovaries. At the beginning of the cycle, the hypothalamus releases Gonadotropin-releasing hormone (GnRH), stimulating the pituitary gland to secrete Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH). FSH promotes the maturation of follicles in the ovaries, while LH triggers ovulation. After ovulation, the ruptured follicle transforms into the corpus luteum, which secretes progesterone to maintain the uterine lining. If pregnancy does not occur, hormone levels drop, leading to menstruation and the start of a new cycle.